1. Field of the Invention
The present invention relates to a non-halogen base gas-barriering coated film suitably used for packing materials for foods and medicines for the purpose of preserving the contents by cutting off various gases such as oxygen, steam and fragrant components.
2. Description of the Related Art
In recent years, plastic films, sheets and the molded and processed products thereof are mainly used for packing materials for the purpose of preserving the contents because of transparency, light weight and economical efficiency. Performances required to plastic films used for packing foods, medicines and cosmetics include a barriering property against various gases, a transparency, a retort treating resistance, a bending resistance, a flexibility and a heat sealing property, and the high barriering property against oxygen and steam is particularly required for the purpose of preserving a performance and a quality of the contents.
In general, a gas barriering property of plastic films is not high so much, and a method in which a polyvinylidene chloride (PVDC) resin is coated has so far mainly been used as means for providing these films with a gas barriering property. However, it is regarded as a problem that a PVDC-coated film prepared by this method contains a halogen atom and therefore generates hazardous gas such as dioxin in incinerating, which is likely to cause environmental rupture.
Known as an alternative technique for this are an ethylene vinyl acetate copolymer-saponified product (EVOF resin) film, a polyvinyl alcohol (PVA)-coated film and an inorganic-deposited film obtained by depositing silica and alumina on a flexible polymer film. However, the EVOH resin film and the PVA-coated film have the problem that if they are exposed to moisture at a high humidity or subjected to boiling treatment or retort treatment, an oxygen barriering property is notably reduced, and the inorganic-deposited film has the problem that since a gas barriering layer is formed by depositing a hard inorganic compound, cracks and pinholes are produced on the gas barriering layer by bending and markedly lower the gas barriering property. Further, such vacuum deposition film requires a large-scaled production facility as compared with those in a coated film and laminated film, and it becomes expensive in terms of a production cost.
On the other hand, coating by a polyurethane resin having a gas barriering property and a gas barriering film having this resin layer are disclosed as a non-halogen base coating technique in an official gazette of Japanese Patent Application Laid-Open No. 98047/2001. However, this polyurethane resin layer does not have an adhesive property between films and therefore can not help being restricted to the same uses as those of gas-barriering film layers which have so far been used. Accordingly, when a gas barriering property is required to packing materials, an adhesive has to be applied in coating a gas barriering layer on a conventional film, so that a laminated film is disadvantageous in terms of a production cost. Further, a film prepared by applying an adhesive is increased in a thickness since an adhesive layer is added to a coating layer, and therefore an influence exerted on the environment by an increase in waste which is regarded as a problem in recent years is inevitably concerned about. Accordingly, a gas-barriering coated film in which a gas barriering performance is compatible with an adhesive performance is strongly desired to be developed in a packing material from the viewpoint of both of the cost and the environment.
An object of the present invention is to provide a non-halogen base gas-barriering coated film which solves the problems described above and has an excellent gas barriering property.